1. Field of Invention
The present invention relates to a pressure gauge glow plug for a diesel engine having a plug body for insertion into a cylinder of the diesel engine, a heating element which is positioned in the plug body, and a pressure sensor, which is positioned, under pretension, between the heating element and the plug body in such a way that the pressure sensor experiences the pressure existing in the combustion chamber of the cylinder, which is transmitted from the heating element.
2. Description of Related Art
A pressure gauge glow plug of this type is known from European Patent Application EP 1 096 141 A3 and corresponding U.S. Pat. No. 6,539,787.
In this known pressure gauge glow plug, the plug body and the heating element are rigidly bonded to one another on the combustion chamber side and the plug body has such a strength that it may radially deform elastically when a pressure is applied to it. The pressure in the combustion chamber of the cylinder acts on the plug body and the heating element, so that the plug body, which is seated solidly in the cylinder of the internal combustion engine, deforms elastically while the heating element moves axially in relation to the plug body. Through this axial motion in relation to the plug body, the pressure sensor, which is under pretension, is unloaded, the difference in the load state between the loaded and the unloaded state being tapped as the signal for the pressure existing in the combustion chamber and analyzed.
The purpose of a pressure gauge glow plug of this type is to act as a cold-start aid for starting the diesel engine at low temperatures and/or for intermediate glowing in the event of unfavorable operating conditions and, in addition, to obtain information about the combustion sequence in the cylinder through the pressure sensor, which may comprise a piezoceramic or a strain gauge, to analyze this information, and to control the combustion sequence accordingly. By using a pressure gauge glow plug of this type, a diesel engine results which may be regulated in regard to the reduction of exhaust gases and consumption.
In a pressure gauge glow plug of this type, not only is the pressure produced in the cylinder relayed via the heating element to the pressure sensor, but also mechanical forces caused by temperature oscillations or thermal loads of the glow plug caused by glowing, by ambient temperature oscillations, etc. are also relayed to the pressure sensor, which then changes its properties, particularly its pretension, which may result in measurement errors.